1. Field of the Invention
The present invention relates to a confocal optical system used for a scanning apparatus, such as a confocal endoscope apparatus, that can display a highly enlarged subject image at high resolution.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2005-80769 discloses a confocal endoscope apparatus that can display a highly enlarged image at high resolution compared to a usual endoscope. In the confocal endoscope apparatus, a scanning fiber is moved along a predetermined course while emitting illumination light toward an observation area. Reflected light or autofluorescence from a point illuminated by the illumination light is made incident on the scanning fiber. The scanning fiber transmits the reflected light or autofluorescence to a light receiving unit, which detects the amount of received light.
To carry out a confocal observation with a confocal endoscope apparatus having the above structure, it is preferable to condense a beam of light with a thick diameter.
In addition, a single mode fiber should be used as the scanning fiber in a confocal observation. However, it is difficult to emit a beam with a sufficiently large diameter from a single mode fiber. Accordingly, a lens unit mounted in the emission end of the scanning fiber needs to include an optical enlargement system.
However, the size of the lens unit increases by including the optical enlargement system. In addition, movement of a point illuminated by the illumination light according to the movement of the emission end of a scanning fiber with the optical enlargement system is much less than it is relative to a scanning fiber without the optical enlargement system. In order to capture an image of a subject of considerable size, the emission end needs to be moved substantially. Accordingly, it is difficult to manufacture a thin insertion tube that includes the above lens unit and scanning fiber.